Method of adaptively adjusting the coefficients of a digital filter in an echo canceller
First Claim
1. A method of adaptive echo compensation with a digital filter whose number n of filter coefficients (ci), or briefly its set of filter coefficients (C(j)), is calculated in accordance with the Normalized-Least-Mean-Square algorithm, in a transmission system in which a coupling occurs between a signal path in the receiving direction and a signal path in the transmitting direction, characterized in thatthe set of filter coefficients (C(j)) is compared to an envelope curve (H(j)),an error measurement (F(j)) is calculated from the variation between the values of the set of filter coefficients (C(j)) and those provided by the envelope curve (H(j)),only the set of filter coefficients (C(j)) in which the error measurement (F(j)) drops below a threshold value is used further to adjust the digital filter.
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Abstract
Digital filters are used to compensate for echoes in a transmission system in which unwanted couplings occur between a signal value in the receiving direction and a signal value in the transmitting direction. The correct adjustment of the filter coefficients has a considerable influence on the achievable echo compensation. Disturbance signals such as background noises, nonlinear effects in A/D converters or an active local speaker can briefly change the adjustment of the filter coefficients in a way so that the digital filter does not compensate for the echoes and causes additional echoes in unfavorable cases. In accordance with the invention a set of filter coefficients (C(j)) are weighted with an envelope curve (H(j)) and an error measurement (F(j)) is determined therefrom. Depending on the magnitude of the error measurement (F(j)), the filter coefficients (ci) are used for further processing or are discarded. The pertinent arrangement comprises a first digital filter (1) for which the filter coefficients (ci) are continuously calculated in accordance with the NLMS algorithm. These filter coefficients (ci) are stored, weighted and the best values are used to adjust a second digital filter (7) whose output signal (9) is subtracted from the echo-affected signal, creating an echo-free output signal (10) and thus significantly increasing the quality of a natural and undisturbed transmission, even with short-time disturbances.
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12 Claims
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1. A method of adaptive echo compensation with a digital filter whose number n of filter coefficients (ci), or briefly its set of filter coefficients (C(j)), is calculated in accordance with the Normalized-Least-Mean-Square algorithm, in a transmission system in which a coupling occurs between a signal path in the receiving direction and a signal path in the transmitting direction, characterized in that
the set of filter coefficients (C(j)) is compared to an envelope curve (H(j)), an error measurement (F(j)) is calculated from the variation between the values of the set of filter coefficients (C(j)) and those provided by the envelope curve (H(j)), only the set of filter coefficients (C(j)) in which the error measurement (F(j)) drops below a threshold value is used further to adjust the digital filter.
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